Modular Retaining Wall Installation & Guide | Western Interlock
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Paving Stones and Retaining Wall Systems Made for the Northwest.

Modular Retaining Wall Installation

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Modular Retaining Wall is an easy do-it-yourself retaining wall. The individual blocks interlock together without any mortar or pins. Here are some helpful hints to enable you to achieve the beauty you desire in a retaining wall project. For more assistance, contact our helpful office staff.

General installation guidelines apply to all lip-type retaining walls.

Step 1:
Planning your Project
Prepare a layout for your modular retaining wall project. To help plan the number of blocks you will need for your project, multiply the face area times two to figure the number of blocks required. For help measuring curves, lay a garden hose along the proposed length of your wall; then straighten it out and measure its length.

Step 2:
Preparing the Base
Excavate the soil in the location where the retaining wall is to be, assuring 6″ of space on the rear side of the wall for gravel backfill. Dig a trench for the first course of stone 16″ wide by 6″ deep. Fill the first 3″ to 4″ of the trench with ¾” minus gravel and compact well, making sure that the gravel is level.

Step 3:
Setting the Bottom Course
Set the first block on the gravel base. It will be necessary to dig out a small amount of the compacted base for the lip on the bottom rear of the block so that the leveling portion of it is level in all directions. Settle the block into the gravel base, using a heavy rubber mallet to seat it firmly. Set adjacent blocks in the same manner, keeping them level with each other. Place ¾” minus gravel behind the first course and compact.

Step 4:
Setting Remaining Courses and Back Filling
Set the next course, making sure that the joints do not line up with the previous course. Backfill with gravel and compact again before setting the next course. Place all the remaining courses until the wall has reached your desired height. As the courses rise, the wall will have a tendency to lean back. Use the compacted gravel backfill to keep it straight by tamping lightly behind the rear of the stones, maintaining the same vertical angle from top to bottom.

Step 5:
Finishing the Wall
Set the top course and backfill to within 3″ of the top. Finish backfill area with soil to the desired height. The top course can either be held in place by gravity or fixed with an approved flexible adhesive. Modular walls can also be capped off with special caps or our Arena Stone held in place by mortar.

76 Modular Wall Install

Currently applies to the following products:

  • Slope Block
  • Jumbo Nursery Stone
  • Nursery Stone

Typical Modular Installation Diagrams


  • A drainage pipe can be used as shown in illustrations if there is a problem with excessive water in the retained area.
  • The standard wall angle set back is 12 degrees. If a different angle is required, then the angle the first course is set at must be adjusted to accommodate the different angle. This angle is maintained as the following courses of stone and gravel are placed.
  • Engineering is required on walls over 4’ high. Call manufacturer for details.
  • Cutting will be necessary for 90 degree corners and possible for the offsets on the different courses.